A refrigeration cycle is utilized to chill water for use in one or more processes. The cycle includes an evaporator through which water to be chilled is passed and in which expanding coolant is utilized to draw heat from the water. The coolant is supplied to the evaporator over a coolant circuit containing a compressor, a condenser, and a control valve for controlling the amount of cooling effect.
To conserve energy, it is desirable to optimize chilled water temperature by critically controlling the flow of coolant and the use of power in the coolant cycle as well as the chilled water cycle. This requires a properly integrated compressor control.
As is known, there are two major control loops in a compressor. The one loop is used for controlling a process variable (such as chilled water temperature) by manipulating the compressor load. The other loop is used for protecting the compressor against surging; namely, surge control for a stable operation. These two control loops, when independently operated in separate nonintegrated loops, interact and cause unnecessary oscillations. When the compressor operates near the surge line, these oscillations become damaging.
There are known surge controls based on both surge detection and compressor load variation. However, the surge control as used to initiate compressor load variation rather than integrate the surge control with the load demand of the compressor. An example of such a surge control system may be found in U.S. Pat. No. 4,142,838. Nor are there any known control systems which coordinate compressor operation with surge protection to insure optimized operation of the two for optimized chilled water delivery.